Vemurafenib currently has Food and Drug Administration approval for the treatment of BRAF V600E+ metastatic melanoma in adults, but recent discoveries of BRAF V600E in more than half of tested Langerhans cell histiocytosis lesions have prompted clinical trials of vemurafenib therapy for children with refractory, multisystem Langerhans cell histiocytosis.
A breakthrough in understanding the pathogenesis of LCH occurred in 2010 when a gain-of-function mutation in BRAF (V600E) was identified in more than half of LCH patient samples.
A mutational study by massive sequencing identified the Val600Glu (V600E) BRAF mutation in the Langerhans cell histiocytosis lesions, but no molecular alterations were found in the reticulohistiocytoma lesions.
Here we present an unusual case of a patient with TP53-mutated chronic lymphocytic leukemia (CLL) treated with a PI3Kδ inhibitor evolving to clonally related Langerhans cell histiocytosis (LCH) with acquired BRAF V600E and STK11 mutations and loss of expression of PAX-5 and other examined B cell markers.
Although the BRAF V600E mutation constitutes the majority of molecular alterations in ECD and LCH, only three reported JXG neoplasms, all in male pediatric patients with localized central nervous system (CNS) involvement, are known to harbor the BRAF mutation.